The present invention relates to a valve system.
A valve system of this type is used, e.g., to activate hydraulic consumers of a mobile working machine, such as a wheel loader, a bulldozer, a crawler dozer, a telescopic loader, or an underground loader.
Data sheet RD 64 284/06.00 from Mannesmann Rexroth AG describes an LUDV mobile control block, in which the pressure-medium supply to the consumers is controlled via sections of directional control valves, using one proportional directional valve in each case. It includes one speed part, which is formed by a metering orifice, and a direction part which determines the direction of flow of pressure medium to and from the consumer. An LUDV pressure compensator is assigned to the metering orifice. In a mobile control block of this type, a load-independent flow distribution (LUDV) is given for consumers that may be activated simultaneously. As stated in a highly simplified manner, in LUDV systems of this type, when the activated consumers are under-supplied, i.e., when a pump is unable to meet the desired demand for pressure medium, the pressure differences across all open metering orifices decrease, and therefore the quantities of pressure medium that flow to the activated consumers are reduced by the same proportion. In this manner, it is ensured that individual consumers are not brought to an unwanted standstill. The present invention is not limited to LUDV systems, however.
In the known solution, the proportional directional valve may be moved from a neutral or centered position into the direction of first positions, in which, e.g., a hydraulic cylinder is retracted. When displaced in the other direction, the hydraulic cylinder is extended. Furthermore, the directional-control valve section may be moved into a floating position by switching over a floating-position valve and simultaneously activating the valve spool in the “lower” direction; in the floating position, the two consumer ports and the pressure port are connected to the tank port, and therefore, e.g., a dozer blade of a crawler dozer lies on the ground simply under its own weight. The disadvantage of this solution is that a separate floating-position valve is required.
Publication DE 103 36 684 A1 shows a valve system in which the directional control valve is equipped with four positions (neutral position, raise, lower, floating position) of a valve spool. The term “position” is understood to mean a large number of intermediate positions, in each of which an opening cross section that is active in terms of the functions “neutral”, “raise”, “lower”, and “floating position” may be changed.
DE 196 08 758 A1 discloses a solution, in the case of which a valve spool of the directional control valve may be displaced into five positions (floating position, lower, neutral position, vibration damping, and extend); in the “vibration damping” position, an annular chamber of the hydraulic cylinder that is active in the direction of retraction is connected to the tank.
In none of these solutions is it possible, by displacing the valve spool, to obtain a quick- action function in addition to the functions “neutral setting”, “extend”, “retract”, and “floating position”, in which the pressure medium, which has been displaced out of the contracting pressure chamber of the consumer, e.g., the annular chamber of a hydraulic cylinder, is added to the volumetric flow of pressure medium being supplied to the other pressure chamber of the consumer. To realize a quick-action function of this type in the known solutions, a separate valve device must be provided, via which, when the “quick-action” function is activated, the volumetric flow of pressure medium flowing out of the contracting pressure chamber circumvents the directional control valve and is added to the volumetric flow of pressure medium that is flowing to the pressure chamber which is expanding.